1. Field of the Invention
The specification, the drawings, and the claims of the present application (hereinafter referred to as “this specification and the like”) disclose a semiconductor device, an operation method thereof, and a manufacturing method thereof. Needless to say, embodiments of the present invention are not limited to the fields listed above.
In this specification and the like, a semiconductor device means a device that utilizes semiconductor characteristics and refers to a circuit including a semiconductor element (e.g., a transistor, a diode, or a photodiode), a device including the circuit, and the like. The semiconductor device also means any device that can function by utilizing semiconductor characteristics. For example, an integrated circuit, a chip including an integrated circuit, an electronic component including a packaged chip, and an electronic device including an integrated circuit are examples of a semiconductor device. Furthermore, a memory device, a display device, a light-emitting device, a lighting device, an imaging device, and the like themselves are semiconductor devices. These semiconductor devices each further include a semiconductor device in some cases.
2. Description of the Related Art
A basic current source circuit of a CMOS circuit can include a current mirror. A current source circuit (source current source) can be formed using a current mirror circuit including p-channel transistors (PMOS current mirror circuit); a current sink circuit (sink current source) can be formed using a current mirror circuit including n-channel transistors (NMOS current mirror circuit). In this specification, a p-channel transistor and an n-channel transistor are referred to as PMOS and NMOS, respectively, for convenience.
For example, Patent Document 1 discloses a current amplifier circuit which can selectively output a source current that is set in a PMOS current mirror circuit or a sink current that is set in an NMOS current mirror circuit and whose output current level can be changed in accordance with an input signal.
A variety of semiconductor devices that take advantage of an extremely low off-state current of a transistor whose channel formation region includes an oxide semiconductor (hereinafter, the transistor is referred to as an oxide semiconductor transistor or an OS transistor) have been proposed. For example, Patent Document 2 discloses a memory circuit including an OS transistor.